High speed electrostatographic copying machines use different types of image receptors. Photoreceptors usually comprise a substrate bearing at least one photoconductive coating layer. One such photoreceptor is the drum type. In the manufacture of drum type photoreceptors, at least one photoconductive layer is coated on a cylindrical substrate by any of a variety techniques, e.g. vacuum coating, dip coating, spray coating, spinner coating, bead coating, wire bar coating, blade coating, roller coating, and curtain coating. These coating techniques, however, are imprecise in that the photoconductor can be coated in areas where no coating is required or desired
For instance, in dip coating methods, a drum substrate is vertically maintained on its axis and then successively dipped in a chemical bath containing an organic photoconductive coating material. The dipped substrate is vertically withdrawn from the bath at a speed that will give a desired thickness for the organic photoconductive coating layer. The process is sometimes repeated to obtain a substrate drum having a plurality of organic photoconductive coating layers. With each dipping, however, a bead of coating material can form at the bottom end of the drum substrate. Bead formation is undesirable because it interferes with components such as charging devices, developer housing, etc., that maintain their interface separation with the photoreceptor by contacting and riding on the end of the photoreceptor. Consequently, the bead of material must be removed from the bottom edge of the photoreceptor. Additionally, coating material may form on the inside of the drum, which interferes with the subsequent placement and gluing of flanges.
Conventionally, a bottom edge wipe method is used to remove the excess photoconductive coating material using environmentally harmful chlorinated solvents such as chlorobenzene, trichloroethane and trichloroethylene in an automated process. A bottom edge wipe method entails causing the bottom (about 1 cm) of the photoreceptor to come into contact with brushes or webs containing a solvent capable of removing the photoconductive coating material. The brushes or webs contact the inside and outside of the drum to remove the excess coating material. The brushes and/or the photoreceptor is/are rotated to remove the excess photoconductive coating. When several coatings are required, each coating is often removed from the bottom of the drum before the next coating is applied because different solvents are often required for each layer. Complex machinery must be activated and environmentally unsafe solvents (which must be eventually disposed of in an environmentally safe but expensive way) used for each layer. Moreover, one must endure defects such as edge gouges, splashes, incomplete wipes, etc. that result when such machinery malfunctions. As a result, bottom edge wipe methods are cumbersome, inefficient, often produce photoreceptors of unacceptable quality, and require routine maintenance of equipment. This further results in increased activity in the clean room and ultimately slows down the manufacturing process. Further, bottom edge wipe methods are not always successful, requiring an extra step of hand wiping with the same environmentally incompatible chlorinated solvents. According to the present invention, bottom edge wipe can be performed outside of the clean room, without the use of complex machinery and in fewer steps by removing all coating layers in one pass and without the use of environmentally incompatible or harmful solvents.
Various methods have been proposed for separating photoconductive coating layers from substrates. One such method is disclosed in U.S. Pat. No. 3,460,296, to C. A. Dittmar, wherein a hard coating material is removed from a relatively soft substrate by impacting the hard coating with plastic beads having a modulus of elasticity less than the modulus of elasticity of the relatively soft substrate. This method, however, necessarily destroys the photoconductive layer and occasionally damages the substrate.
Another method is disclosed in U.S. Pat. No. 4,501,621, to Abe et al., wherein a coating layer, such as a selenium coating layer, is removed from a substrate by producing cracks in the layer, introducing a volume expansive material into the cracks and then causing the volume expansive material to expand, thereby dislodging the coating layer from the substrate. This method, however, can undesirably destroy the photoconductive coating layer, as well as the metallic substrate sought to be used as a datum or point of reference for other devices found in electrostatographic copiers.
U.S. Pat. No. 5,085,732, to Nakamura et al., discloses a method for removing an amorphous selenium containing photoconductive layer from an electrostatographic photoreceptor by treating the photoreceptor with an aqueous solution of sodium sulfide or sodium thiourea. These chemicals require special treatment before disposal and will not remove many organic coatings.
Other methods include cutting the photoconductive coating layer from the metallic substrate; exfoliating the coating layer by repeated heating and cooling; exfoliating the coating layer by high pressure hot water ejected from a nozzle; heating the coating layer under vacuum to vaporize it; and heating the coating layer followed by chemical treatment. Each of these known methods, however, has residual problems. For example, some of the methods evolve dust or emit harmful vapors or poisonous substances. Some of these methods use environmentally incompatible solvents. And some of these methods involve heat and solvents which undesirably damage the photoconductive layer and the underlying substrate. Moreover, heating a photoreceptor may drive off other chemicals and produce hazardous fumes.